Beam Measurements of the Longitudinal Impedance of the CERN Super Proton Synchrotron Alexandre Samir Lasheen To cite this version: Alexandre Samir Lasheen. Beam Measurements of the Longitudinal Impedance of the CERN Super Proton Synchrotron. Accelerator Physics [physics.acc-ph]. Université Paris Saclay (COmUE), 2017. English. NNT : 2017SACLS005. tel-01565969 HAL Id: tel-01565969 https://tel.archives-ouvertes.fr/tel-01565969 Submitted on 20 Jul 2017 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. NNT : 2017SACLS005 THÈSE DE DOCTORAT DE L’UNIVERSITÉ PARIS-SACLAY PREPARÉE À L’UNIVERSITÉ PARIS-SUD ÉCOLE DOCTORALE N°576 Particules Hadrons Énergie et Noyau : Instrumentation, Image, Cosmos et Simulation (PHENIICS) Spécialité de doctorat : Physique des accélérateurs Par M. Alexandre Samir Lasheen MESURESDEL’IMPÉDANCE LONGITUDINALE AVEC LE FAISCEAU DU CERN SUPER PROTON SYNCHROTRON Thèse présentée et soutenue à Orsay, le 13 Janvier 2017 Composition du jury: Dr. Guy Wormser, LAL, Président du jury Prof. Costel Petrache, CSNSM, Directeur de thèse Dr. Elena Shaposhnikova, CERN, Co-directrice de thèse Prof. Jean-Marie De Conto, LPSC, Rapporteur Prof. Mauro Migliorati, Univ. La Sapienza, Rapporteur Dr. Elias Métral, CERN, Examinateur Dr. Ryutaro Nagaoka, SOLEIL, Examinateur Dr. Olivier Napoly, CEA, Examinateur À ma famille, à Marie. Un voyage de mille lieues commence toujours par un premier pas. Acknowledgements First and foremost, I would like to thank Elena Shaposhnikova for giving me the chance to do my PhD under her supervision. During these three years and since the very first day, her advice and guidance was always relevant and in my interest to progress. Thanks for sharing with me your immense knowledge, for your kindness and your endless curiosity that I will keep as a great source of inspiration as a researcher and for my life in general. I would like also to thank Costel Petrache, for accepting to be my supervisor on behalf of the university. Costel was also my supervisor as a master’s degree student, and supported me when I applied for a PhD at CERN. Thanks for always supporting me for my last steps as a student and the first ones as a researcher, allowing me to do this exciting work. I am thankful to the members of the jury: Prof. Jean-Marie De Conto and Prof. Mauro Migliorati for accepting the important task to review the manuscript as referees, Dr. Elias Métral, Dr. Ryutaro Nagaoka and Dr. Olivier Napoly as members of the examining committee and Dr. Guy Wormser as president of the jury. Thanks for your interesting questions and remarks on my work. The work presented here would not have been possible without the help of many colleagues. Since my arrival, I could always count on my exceptional office mates, Theodoros Argyropoulos and Juan Esteban Müller. Theo and Juan showed me all the tricks I needed to know to be efficient in my work, as well as being remarkable people. Thanks to both of you for making every working day enlightening, enjoyable and for your friendliness. In that respect, I would also like to thank Helga Timko for introducing me to the topic at my arrival, and Joël Repond to whom I introduced the topic in the end of my PhD. Special thanks to Thomas Bohl and Steve Hancock, for helping me to tame the RF systems of the whole injector chain and showing me all I needed to know to perform autonomously beam measurements. Thanks for the countless hours you devoted me in the SPS BA3 Faraday cage and in the CPS island in the CCC, to share your knowledge with me. My work was done in the Beams and RF section at CERN. I would like to thank all the members of this section where I felt well integrated and part of a great project, with special thanks to Simon Albright and James Mitchell for proofreading my thesis. I would like also to thank the students passing by and always bringing a great atmosphere. The simulation code BLonD was used for all the simulations done during my PhD. The development of this code was the result of a fruitful collaboration, and I would like to thank Danilo Quartullo and Konstantinos Iliakis for maintaining and optimising the code, as well as Helga, Juan, Joël and Simon for their development. i Acknowledgements The work presented in this thesis relies on the important work of the impedance team at CERN. Extensive efforts were devoted to develop the SPS impedance model, mainly by Jose Varela, Benoit Salvant, Carlo Zannini, with additional contributions from Thomas Kaltenbacher, Patrick Kramer, Christine Vollinger, Toon Roggen and Rama Calaga. Many thanks to all of you and for the fruitful discussions. All the measurements presented in this thesis were made possible thanks to the help of Giovanni Rumolo and Hannes Bartosik as MD coordinators. Thanks for your confidence in my work, and for the beam time you gave me. I am also thankful to the SPS and CPS operation teams, for giving me their time to adjust the machine parameters. Pour finir je tiens à remercier ceux par qui tout a commencé. Merci à mes parents et ma sœur pour leur soutien inconditionnel depuis mes tout premiers pas. Merci à toi Marie de m’avoir accompagné au quotidien et d’avoir donné tout son sens à ma vie. Merci finalement à tous ceux qui ne sont pas nommés ici mais qui ont contribué à leur façon, par leurs encouragements, leur amitié, et leur bienveillance... A.S.L. ii Abstract One of the main challenges of future physics projects based on particle accelerators is the need for high intensity beams. However, collective effects are a major limitation which can deteriorate the beam quality or limit the maximum intensity due to losses. The CERN SPS, which is the last injector for the LHC, is currently unable to deliver the beams required for future projects due to longitudinal instabilities. The numerous devices in the machine (accelerating RF cavities, injection and extraction magnets, vacuum flanges, etc.) lead to variations in the geometry and material of the chamber through which the beam is travelling. The electromagnetic interaction within the beam (space charge) and of the beam with its environment are described by a coupling impedance which affects the motion of the particles and leads to instabilities for high beam intensities. Consequently, the critical impedance sources should be identified and solutions assessed. To have a reliable impedance model of an accelerator, the contributions of all the devices in the ring should be evaluated from electromagnetic simulations and measurements. In this thesis, the beam itself is used to probe the machine impedance by measuring the synchrotron frequency shift with intensity and bunch length, as well as the line density modulation of long bunches injected with the RF voltage switched off. These measurements are compared with macroparticle simulations using the existing SPS impedance model, and the deviations are studied to identify missing impedance sources and to refine the model. The next important step is to reproduce in simulations the measured single bunch instabilities during acceleration, in single and double RF system operation. Thanks to the improved impedance model, a better understanding of instability mechanisms is achieved for both proton and ion beams. Finally, as the simulation model was shown to be trustworthy, it is used to estimate the beam characteristics after the foreseen SPS upgrades the High Luminosity-LHC project at CERN. Key words: particle accelerators, longitudinal beam dynamics, beam-based measurements, CERN SPS, beam coupling impedance, beam instabilities iii Résumé Un des défis pour les futurs projets en physique basé sur les accélérateurs de particules est le besoin de faisceaux à hautes intensités. Les effets collectifs sont cependant une limitation majeure qui peuvent détériorer la qualité du faisceau ou limiter l’intensité maximale à cause des pertes. Le CERN SPS, qui est le dernier injecteur pour le LHC, n’est actuellement pas en mesure de délivrer les faisceaux requis pour les futurs projets à cause des instabilités longitudinales. Les nombreux équipements dans la machine (les cavités RF accélératrices, les aimants d’in- jection et d’extraction, les brides de vide, etc.) entrainent des variations dans la géométrie et les matériaux de la chambre dans laquelle le faisceau transite. Les interactions électroma- gnétiques internes au faisceau (charge d’espace) et du faisceau avec son environnement sont représentées par une impédance de couplage qui affectent le mouvement des particules et mènent à des instabilités pour des intensités élevées de faisceau. Par conséquent, les sources d’impédance critiques doivent être identifiées et des solutions évaluées. Pour avoir un modèle d’impédance fiable d’un accélérateur, les contributions de tous les équipements dans l’anneau doivent être évaluées à partir de simulations et de mesures électromagnétiques. Dans cette thèse, le faisceau lui-même est utilisé comme une sonde de l’impédance de la machine en mesurant le déplacement de la fréquence synchrotronique avec l’intensité et la longueur du paquet, ainsi que la modulation de longs paquets injectés avec la tension RF éteinte. Ces mesures sont comparées avec des simulations par macroparticules en utilisant le modèle d’impédance du SPS existant, et les déviations sont étudiées pour identifier les sources d’impédance manquantes pour raffiner le modèle. L’étape suivante consiste à reproduire en simulations les instabilités mesurées pour un paquet unique durant l’accélération.